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Spitfire MkIV - rear end knocking mystery


cwillst
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I have a 1972 Spitfire, restored by a PO about 10 years ago, the drive shaft UJ's replaced some 8 years ago, some 3000 miles of travel since then. In the last couple of years the car has developed a rear end knocking noise that is relational to road speed. Only noticeable at low speeds and mostly appears once car has run a mile or so. I have not been able to trace it. I have a tame professional mechanic who had his own garage with years of experience with classic cars. He has not been able to trace it, mind you it seems to dissappear for a few miles once he has had  his hands on checking the rear end. He tells me not to worry, old cars have rattles and knocks. I still drive it but am concerned that it will reveal itself when something brakes. My question to the forum is whether there is something about the Spitfire rear end drive geometry that could mask worn UJs or UJ float from such a mechanic?  He is very experienced with Minis. Has restored cars and at least one GT6 so does know his stuff. I am going to get him to do my pre-season safety check soon, so are there any suggestions the forum could give me to pass on.  I have waded through this topic reading all the knocking stories! The one that seems most likely is whether it needs wider gauge clips to stop end float. 

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think thats about right,

nice to see youve done some homework

low speed rythmical with the wheel rotation has all the traits of UJ float,

loose hub nut,& loose wheel nuts, cracked wheel nave ,   also worth close examination 

if it disappears after being jacked , have a think about trunion and tie rod bushes

if you can jack the car , run in gear . is the drive shaft running true ...bent ones give odd problems 

if someone drives past  you slowly can you hear it outside ?

if checking UJ float/lift get the suspension lifted to running height , left hanging will hide   UJ  end float

Pete

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Thanks Pete - again.

I will discuss with my tame mechanic. Before that I will have a listen from outside. I think it is that noisy that it can be heard bur you know how well sounds travel inside cars.

I will confirm back when / if we solve trhis. 

 

Tim

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The rear spring loads up the uj's making any free play difficult to diagnose.

But the simple solution may he to see if oversize circlips can be fitted. Done by taking a circlip out, giving the cup a tap to push it in and see if an oversize clip will fit. If so try the oppositr side, it may accept another. Keep going until all the cups are checked.

The problem is than some uj's are supplied with undersize clips. Helpful or what. Oversize ones pretty cheap and available from canley and others. I used to keep a selection when my shafts had uj's...

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  • 2 months later...

We finally traced and fixed the problem. It was warn uj  on the drivers side plus leaky wheel bearing. The cups were rotating in the yoke so I  ended up replacing the whole assembly, and the diff because there was a lot of play . Great to have the car back on the road again but my wallet is lighter too.

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You cant check backlash in the diff by feeling the  play this is just the uncontrolled clearance meshing of the sun and planet gears of the  actual  differential assembly its   play is normal,and not overly important   1/8 of a turn on the prop free movement is pretty standard it just takes up the crude diff gear backlash it will increase as the  thrusts wear but its not adjustable

Crown wheels backlash needs a dial indicator to check it and you might detect it with very light feely fingers on the coupling

most will not detect it

Pleased you have solved it but the diff was probably normal .

Pete

 

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I get what you say about the backlash. I did get someone who only works on and restores triumphs to check it for me and I took his advice. He did say it was the worst case of backlash he had come across. The diff also had a bad leek but that alone doesn't justify the swapp. The gear change feels a lot better now that the slack has gone as. But from whatyou say, it may have been a costly exercise that was not really needed.

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Maybe theres a bit more movement than on my diff but the noise is certainly very similar. I too had oil leaking from the front seal but cleaned out the vent jiggle pin and luckily its now not longer worth worrying about👍 

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that 'slack;  is probably better than 'normal'   

most diffs of  any make of this type of design have that ...there are only two diff gears  two planets  , bigger diffs have 4 planets

its a rough design  whilst  it does transmit load , has nowt to do with noise , and only turns on corners or doing wheel spins on eg.  ice 

that play is inconsequential  if your guy thinks its the worst i would change the guy ,  as thats poor advice

Pete

'

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but the cups are only a light press fit they will rotate on many a UJ due to the forces  .  20 -40 years of slow will eventually make a slack fit 

having said that normal clearances will allow slow rotation , excess worn or stretched yokes and rattling good fit is not recommended 

they do need to be the correct size /fit.   

staked cups wont rotate but you dont want them

Pete

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